<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<link rel="stylesheet" href="css/bootstrap4.1.1.css" />
		<script type="text/javascript" src="js/bootstrap-4.1.1.min.js" ></script>
		<script type="text/javascript" src="js/jquery3.2.1.min.js" ></script>
	</head>
	<body>
		<ul class="nav nav-pills">
    <li>
        <a href="#">A</a>
    </li>
    <li class="dropdown">
        <!-- span标签 是添加一个下三角的图标 -->
        <a href="#" class="dropdown-toggle" data-toggle="dropdown">B<span class="caret"></span></a>
        <ul class="dropdown-menu">
            <li><a href="#">B1</a></li>
            <li><a href="#">B2</a></li>
            <li><a href="#">B3</a></li>
            <li><a href="#">B4</a></li>
        </ul>
    </li>
    <li><a href="#">C</a></li>
</ul>

	</body>
</html>
